The recovery of various metals from scrap material has become increasingly important in light of the growing scarcity of primary raw materials and their increasing cost. In addition, recycling also helps to reduce ecological trauma. Various methods have been developed to recover various metals from different mixtures. For example, in U.S. Pat. No. 3,666,442 to Layne et al, a method of obtaining a beryllium enriched material by comminuting an aluminum-beryllium alloy is disclosed. In this method, the comminuted alloy produces a coarse particulate fraction of an aluminum-beryllium eutectic composition and a fine particulate fraction of beryllium which is then easily separated out by screening. Another method, used for separating zinc and aluminum from iron and copper based alloys, is disclosed in U.S. Pat. No. 3,605,243 to Oster. In this method, the scrap mixture is first rolled to reduce the size of the particles and then tumbled. The tumbling causes the zinc and aluminum to break away from the iron and copper alloys from which it can be separated easily.
There has also been disclosed in the prior art methods for embrittling scrap material so that it can be easily separated. For example, in U.S. Pat. No. 3,885,744 to Drage, a method for freezing scrap at cryogenic temperatures is disclosed in which the frozen scrap is then crushed to a smaller size amenable to magnetic and gravity separation. Also disclosed in U.S. Pat. No. 4,123,294 to Hanink is a method of separating ferritic steel and ductile iron from other valuable metals by carburizing the scrap to embrittle the iron and steel. The scrap is then pulverized to reduce the iron and steel to a powder which is easily removed by screening.
In the secondary aluminum industry there exists a significant volume of aluminum scrap containing both wrought aluminum and cast aluminum. Such mixed scrap comes from various sources such as junked automobiles, urban waste and scrap appliances. Generally, wrought aluminum is fairly pure aluminum while cast aluminum has a high silicon content. In many instances it is desirable that wrought and cast aluminum be separated from each other.
A number of possible methods for separating cast and wrought aluminum have been considered and tested by applicants. These methods included eddy current techniques, chemical spotting for subsequent color sorting, and reshredding and screening. However, the results of these considerations and tests indicate that these methods apparently have little or no beneficial effects in separating cast and wrought aluminum.